Inverse prostheses of the shoulder are known, for the articulation of a sphere attached to the scapula in a mating cavity obtained in the upper part of the humerus, which inversely reproduce the gleno-humeral anatomy. Normally, inverse prostheses are used in the event of serious muscular degeneration of the shoulder, particularly of the rotator cuff muscles. The degeneration of such muscles causes a prevalent action by the deltoid, which tends to draw the humerus upwards, consequently making the humeral bone head, or possible artificial head, move upwards, with the risk of making it knock against the protrusion which prolongs the spine of the scapula, known as acromion.
Starting from the idea of eliminating the humeral head, inverse prostheses comprise, as elements associated with the humerus, a concave shaped humeral seating including a relative attachment shaft implanted in the humerus.
The humeral seating defines the articulation for a spherical body attached to the glenoid cavity, which is provided in a single body with a pin for direct attachment in the glenoid cavity, or to a support previously attached to said glenoid cavity.
One shortcoming of known inverse prostheses is that the attachment pin of the aforementioned spherical body is difficult to insert into the glenoid cavity, or into the relative support element, previously applied, due to the extremely limited spaces available; this is an obstacle to precise positioning and a limit to the surgeon's operating possibilities.
A further disadvantage of known inverse prostheses is that the position of the spherical body cannot be oriented or translated as desired with respect to the wall of the glenoid cavity where the relative pin is attached.
One purpose of the invention is to achieve a prosthesis for the articulation of the shoulder wherein the implantation of an inverse prosthesis will allow the spherical body to be assembled easily and precisely in the glenoid cavity, facilitating the work of the surgeon.
Another purpose of the invention is to achieve a prosthesis of the shoulder in an inverse configuration wherein it is possible to select the orientation and position of the spherical body with respect to its axis of implantation in the glenoid cavity, in relation to the presence of non-regular spaces between the glenoid cavity and the head of the humerus.
The Applicant has devised, tested and embodied the present invention to achieve these purposes and other advantages, and to overcome the shortcomings of the state of the art.